1. Field of the Invention
The invention encompasses the clinical uses of zinc complexes of natural amino acids, such as those natural amino acids with basic side chains, for example L-arginine, lysine, ornithine, and histidine, and other alpha amino acids of natural occurrence, in treating elevated copper caused toxicities, in the maintenance therapy of Wilson's disease, and also in combination with other copper binding drugs, like penicillamine, trientine and thiomolybdates. These zinc complexes may similarly be used to treat inflammatory and fibrotic diseases such as pulmonary fibrosis, liver cirrhosis, hepatitis C, kidney disease, and Alzheimer's disease.
2. Description of Related Art
Zinc salts (acetate or sulfate) are anti-copper agents used in the lifetime management of Wilson's disease, which is an inherited disorder and causes abnormal copper accumulation in the body. This copper accumulation causes severe toxicity in the liver, brain and other vital organs of its afflicted patients. Its onset is at a relatively young age, and is fatal, if not diagnosed early and treated correctly. (See Wilson's Disease, A Clinician's Guide to Recognition, Diagnosis, and Management, George J. Brewer; Kluwer Academic Publishers, 2001, and references cited therein.) For fast lowering of dangerous copper levels, patients may be acutely treated with either: the potent, yet toxic, classical copper binding drugs like penicillamine or trientine; or the safer tetrathiomolybdates, in addition to customary zinc salts (acetate or sulfate). For maintaining essential copper homeostasis, patients are treated to lifetime therapy of non-toxic zinc salts. (For example, as taught in U.S. Pat. No. 6,855,340.)
Zinc+2 dicationic species exerts its biological effect by inducing the upregulation of the zinc and/or cadmium containing metallothioneins' production in the intestinal cell wall, liver and other tissues [e.g., Induction, Regulation, Degradation, and Biological Significance of Mammalian Metallothioneins; A. T. Miles, G. M. Hawksworth, J. H. Beattie and V. Rodilla; Critical Reviews in Biochemistry and Molecular Biology, 35 (1), 35-70 (January-February 2000); and Metallothionein: the multipurpose protein, P. Coyle, J. C. Philcox, L. C. Carey, and A. M. Rofe; Cellular and Molecular Life Sciences, 59(4), 627-647 (April 2002)]. Metallothioneins are a 61-62 amino acid protein, about a third of which amino acids are cysteines, strongly bind copper, cadmium, and mercury in the food, saliva, and gastrointestinal secretions, preventing their transfer into the blood (see Advanced Inorganic Chemistry, Sixth Edition, F. Albert Cotton, G. Wilkinson, C. Murillo, M. Bochmann, J. Wiley $ Sons, New York, 1999, pp. 628-629). The resulting protein-complexed copper is eliminated in the stool.
Zinc acetate (Galzin®) is approved by the U.S. FDA (1997) for Wilson's disease maintenance therapy in capsules containing 25 or 50 mg of equivalents of zinc, taken three times daily (t.i.d). In some patients, zinc acetate causes gastric irritation and discomfort, which is believed due to it's conversion into zinc chloride in the strongly acidic stomach. About 10% of the patients receiving zinc acetate therapy encounter persistent gastric irritation, burning sensation, and nausea, causing critical patient compliance issues (George J. Brewer in Wilson's Disease, A Clinician's Guide to Recognition, Diagnosis, and Management, George J. Brewer; Kluwer Academic Publishers, 2001, pp. 55-56).
Zinc sulfate is also used, but it causes even more patient discomfort (Hoogenraad T U. Wilson's Disease. In: Warlow C P, Van Gijn., J. Eds., Major problems in Neurology Vol. 30, London: W.B. Saunders Co. 1996).
The initial undesirable effects of zinc salts are exacerbated as the drug is taken on an empty stomach or in-between meals. Usually it takes several days or weeks before zinc acetate therapy is tolerable to the patient (Wilson's Disease, A Clinician's Guide to Recognition, Diagnosis, and Management, George J. Brewer; Kluwer Academic Publishers, 2001, p. 57).
Complexes of arginine and bisarginine with Mg+2, Cu+2, and Zn+2 are reported to be useful in ameliorating chronic essential hypertension, cerebral vascular disease, glaucoma, wound healing, acute and chronic inflammation, and Alzheimer's disease (see U.S. Pat. No. 6,359,007).
Therefore, an alternative form of zinc delivery without the gastric side-effects would be beneficial to patients of Wilson's disease, and in other diseases requiring safe, long-term prevention of copper accumulation and resulting toxicities.